Methods for identifying and using inhibitors of casein kinase 1 epsilon isoform for inhibiting the growth and/or proliferation of myc-driven tumor cells

ABSTRACT

In one aspect, the invention provides a method for inhibiting the growth and/or proliferation of a myc-driven tumor cell comprising the step of contacting the tumor cells with a CSNK1ε inhibitor. In another aspect, the invention provides a method of treating a subject suffering from a tumor comprising myc-driven tumor cells, comprising administering to the subject an amount of a composition comprising a CSNK1ε inhibitor effective to inhibit the growth and/or proliferation of the tumor cells.

RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/321,414, filed Apr. 6, 2010, which is herein incorporated by reference in its entirety.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

This invention was made with U.S. Government support under grant number AG026661 awarded by the National Institutes of Health. The U.S. Government has certain rights in this invention.

FIELD OF THE INVENTION

The invention generally relates to methods for identifying and using anticancer therapeutic agents and, more particularly, to methods for identifying inhibitors of casein kinase 1ε-isoform (CSNK1ε) for inhibiting the growth and/or proliferation of MYC-driven tumor cells.

BACKGROUND OF THE INVENTION

Cancer, namely the uncontrolled proliferation of cells, remains a significant health problem worldwide. Although significant advances have been made in the detection and therapy of various cancers, no universally successful method for prevention or treatment is currently available. Current therapies are generally based on a combination of chemotherapy, surgery, or radiation to selectively destroy or remove the proliferating cells. However, these treatments often prove to be inadequate in many patients. Consequently, recent emphasis has focused on personalized treatment of the cellular and genetic causes of specific cancers.

Cancer is the result of the accumulation of multiple genetic mutations, which result in the activation of oncogenes and/or the inactivation of tumor associated suppressor genes. It is the differential expression of these critical genes and their downstream effectors that enables cells to override the controls on the cell cycle and to initiate unchecked proliferation. Although many genetic mechanisms underlying carcinogenesis have been elucidated, the products of many known oncogenes promote essential functions in healthy cells, such as promotion of the cell cycle and cell growth. Thus, many oncogenes and/or oncoproteins are problematic targets for directed cancer treatment because of the toxicity resulting in normal cells. Therefore, there remains a need to identify drug targets associated with oncogene function, wherein treatment of the targets has minimal negative effect on healthy cells.

SUMMARY OF THE INVENTION

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

In one aspect, the invention provides a method for inhibiting the growth and/or proliferation of a myc-driven tumor cell comprising the step of contacting the tumor cells with a CSNK1ε inhibitor.

In another aspect, the invention provides a method of treating a subject suffering from a tumor comprising myc-driven tumor cells, comprising administering to the subject an amount of a composition comprising a CSNK1ε inhibitor effective to inhibit the growth and/or proliferation of the tumor cells.

In another aspect, the invention provides a method for identifying compounds capable of inhibiting proliferation of a myc-driven cancer cell. The method according to this aspect of the invention comprises: (a) contacting a myc-driven cancer cell line expressing CSNK1ε with a candidate compound in cell culture; and (b) determining at least one of: (i) the level of WNT expression or activity in the presence and absence of the candidate compound, or (ii) the level of SHH expression or activity in the presence and absence of the candidate compound, or (iii) the level of CSNK1ε expression or activity in the presence and absence of the candidate compound, wherein a decrease in the expression level or activity of WNT; and/or a decrease in the expression level or activity of SHH, and/or a decrease in the expression level or activity of CSNK1ε in the presence of the candidate compound is indicative of a compound that inhibits proliferation of a cancer cell.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings.

FIG. 1A is a Western Blot illustrating the protein levels of CSNK1ε in neuroblastoma cells with or without amplified MYCN expression; as described in Example 1;

FIG. 1B is a bar graph illustrating the gene expression levels of CSNK1ε in neuroblastoma cells with or without amplified MYCN expression; as described in Example 1;

FIG. 2 is a bar graph illustrating relative expression of CSNK isoforms in neuroblastoma cells with or without amplified MYCN expression, as determined by qRT-PCR; as described in Example 1;

FIG. 3A is a bar graph illustrating relative levels of CSNK1ε mRNA in neuroblastoma cells with or without Dox induced siRNA silencing, as determined by qRT-PCR; as described in Example 1;

FIG. 3B is a Western blot illustrating relative levels of CSNK1ε protein in neuroblastoma cells with or without induced of siRNA silencing; as described in Example 1;

FIG. 3C is a bar graph illustrating viability of neuroblastoma cells with MYCN amplification (SK-N-BE2 and IMR-32) or without MYCN amplification (SK-N-AS) upon transduction with lentivirus constructs encoding inducible shRNAs targeted at two CSNK1ε sequences and a control sequence; as described in Example 1;

FIG. 3D is a bar graph illustrating the effects of CSNK1ε or MYCN transient knockdown with siRNAs on cell viability in neuroblastoma cells with MYCN amplification (IMR-32) and without MYCN amplification (SK-N-AS), wherein the cells were transfected with siRNA pools specific for each gene (three different duplexes), and viability was assayed 96 hours post-transfection; as described in Example 1;

FIG. 4A is a graph illustrating the viability of neuroblastoma cells with MYCN amplification (IMR-32) and without MYCN amplification (SK-N-AS), as a function of IC261 concentration, wherein viability was assayed at 48 hours after treatment; as described in Example 1;

FIG. 4B is a graph illustrating the viability of neuroblastoma cells with MYCN amplification (IMR-32) and without MYCN amplification (SK-N-AS), as a function of IC261 concentration, wherein viability was assayed at 72 hours after treatment; as described in Example 1;

FIG. 4C is a graph illustrating the viability of neuroblastoma cells with MYCN amplification (IMR-32) and without MYCN amplification (SK-N-AS), as a function of IC261 concentration, wherein viability was assayed at 96 hours after treatment; as described in Example 1;

FIG. 5 shows a series of micrographs illustrating neuroblastoma cells with MYCN amplification (IMR-32) and without MYCN amplification (SK-N-AS) before and 48 hours after exposure to IC261; as described in Example 1;

FIGS. 6A-D graphically illustrate the tumor volume in four mice with engrafted tumors, wherein the tumor cells have amplified MYC expression (SK-N-BE2) and contain lentiviral vectors encoding Dox-inducible shRNAs specific for CSNK1ε or control, wherein tumor volume is expressed over time after shRNA induction by Dox; as described in Example 2;

FIG. 7A graphically illustrates that IC261 treatment inhibits growth of IMR-32 (amplified MYCN expression) xenograft tumors in vivo in comparison to DMSO control treatment; as described in Example 2;

FIG. 7B shows a xenograft mouse before and after treatment with IC261; as described in Example 2;

FIG. 7C shows a xenograft mouse before and after treatment with DMSO (control); as described in Example 2;

FIG. 7D shows immunohistochemical analysis of tumor sections from IC261 and DMSO treatment groups stained with H-E, TUNEL or BrDu; as described in Example 2;

FIG. 8A is a bar graph illustrating that WNT mediated transcriptional response was markedly elevated in neuroblastoma cells with amplified MYCN expression compared to neuroblastoma cells with normal MYCN expression, wherein WNT signaling is expressed as a function of detectable β-catenin reporter signaling; as described in Example 3;

FIG. 8B is a bar graph of WNT signaling as a function of IC261 treatments in neuroblastoma cells that express inducible Tet-MYCN, wherein WNT signaling is expressed as a function of detectable β-catenin reporter signaling; as described in Example 3;

FIG. 8C is a bar graph demonstrating that transient knock-down of β-catenin similarly affected viability of neuroblastoma cells with or without amplified MYCN expression; as described in Example 3;

FIG. 8D is a bar graph illustrating the Sonic Hedgehog (SHH) signaling in neuroblastoma cells with amplified MYCN expression (IMR-32 and SK-N-BE2) and without amplified MYCN expression (SK-N-AS and SH-Sy5Y), wherein SHH signaling is illustrated as a function of Gli/mGLi signaling ratio; as described in Example 3;

FIG. 8E is a bar graph that illustrates the inhibitory effect of SHH inhibitor cyclopamine on the growth of neuroblastoma calls with amplified MYCN expression (IMR-32) and without amplified MYCN expression (SK-N-AS), wherein cells were incubated with 10 μM cyclopamine; as described in Example 3;

FIG. 8F is a bar graph that illustrates the inhibitory effect of SHH inhibitor cyclopamine on the growth of neuroblastoma calls with amplified MYCN expression (IMR-32) and without amplified MYCN expression (SK-N-AS), wherein cells were incubated with 10 μM cyclopamine; as described in Example 3;

FIG. 9A is a Western blot illustrating relative levels of c-MYC protein in several ovarian cancer cell lines; as described in Example 4;

FIG. 9B is a bar graph illustrating the relative expression levels of c-MYC mRNA in several ovarian cancer cell lines as determined by qRT-PCR analysis; as described in Example 4;

FIG. 9C is a bar graph illustrating the gene copy number of c-MYC in several ovarian cancer cell lines as determined by PCR analysis; as described in Example 4;

FIG. 10A is a Western blot demonstrating knock-down of CSNK1ε using lentivirus construct encoding Dox-induced shRNA transfected in ovarian cancer cells with amplified c-MYC expression (COLO720E); as described in Example 4;

FIG. 10B is a bar graph illustrating that inducible shRNAi knock-down of CSNK1ε in ovarian cancer cells with amplified c-MYC expression (COLO720E) causes a decrease in WNT signaling, wherein WNT signaling is measured as a function of β-catenin reporter signaling; as described in Example 4;

FIG. 10C is a bar graph illustrating that inhibition of CSNK1ε kinase function in ovarian cancer cells with amplified c-MYC expression (COLO720E) cultured with increasing doses of IC261 causes a decrease in WNT signaling, wherein WNT signaling is measured as a function of β-catenin reporter signaling; as described in Example 4;

FIG. 11A graphically illustrates the reduction of cancer cell proliferation and viability in mice containing intraperitoneal xenografts of human ovarian cancer cells (TOV112D/Luc) after treatment with IC261 or DMSO control, wherein cancer cell proliferation and viability is determined by Luc imaging; as described in Example 4;

FIG. 11B is a Kaplan-Meier survival plot illustrating improved survival rate after treatment with IC261 in mice containing intraperitoneal xenografts of human ovarian cancer cells; as described in Example 4;

FIG. 12A graphically illustrates the fraction of ovarian cancer cells with amplified c-MYC expression (TOV112D) and without amplified c-MYC expression (CaOV3) at the G1 checkpoint of the cell cycle before and after administration of 1 μM IC261; as described in Example 4;

FIG. 12B graphically illustrates the fraction of ovarian cancer cells with amplified c-MYC expression (TOV112D) and without amplified c-MYC expression (CaOV3) at the G2 checkpoint of the cell cycle before and after administration of 1 μM IC261; as described in Example 4;

FIG. 13A graphically illustrates the relative cell viability of A2780 and A2780-CP70 (cisplatin-resistant) ovarian cancer cells in the presence of increasing doses of cisplatin (CDDP) when cultured in the presence of IC261; as described in Example 4; and

FIG. 13B graphically illustrates the relative cell viability of PE01 and PEO4 (cisplatin-resistant derivative) ovarian cancer cells in the presence of increasing doses of cisplatin (CDDP) when cultured in the presence of IC261; as described in Example 4.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which this invention belongs. Practitioners are particularly directed to Sambrook et al., Molecular Cloning: A Laboratory Manual, 2d ed., Cold Spring Harbor Press, Plainsview, N.Y. (1989); and Ausubel et al., Current Protocols in Molecular Biology (Supplement 47), John Wiley & Sons, New York (1999), for definitions and terms of the art.

It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

As used herein, an “effective amount” or “therapeutically effective amount” of a CSNK1ε inhibitor, or a composition comprising a CSNK1ε inhibitor is an amount sufficient to produce the desired effect, e.g., inhibition of expression or enzymatic (kinase) activity of CSNK1ε in comparison to the normal expression level detected in the absence of the agent, or inhibition of the growth and/or proliferation of a tumor cell. Inhibition of expression or activity of CSNK1ε by an inhibitory agent is achieved when the expression level of the CSNK1ε or protein is about 80%, 70%, 60%, 50%, 40%, 30%, 25%, 20%, 15%, 10%, 5%, or 0% relative to the expression level of the target gene mRNA or protein of a control sample, or when the activity level of the CSNK1ε is about 80%, 70%, 60%, 50%, 40%, 30%, 25%, 20%, 15%, 10%, 5%, or 0% relative to the activity level of CSNK1ε in a control sample without the inhibitory agent.

As used herein, the term to “inhibit the growth and/or proliferation of a tumor cell” means to kill the cell, or permanently or temporarily arrest the growth of the cell. Inhibition of a mammalian tumor cell can be inferred if the number of such cells, either in an in vitro culture vessel, or in a subject, remains constant or decreases after administration of the compositions of the invention. An inhibition of tumor cell proliferation can also be inferred if the absolute number of such cells increases, but the rate of tumor growth decreases.

As used herein, “subject” refers to an organism or to a cell sample, tissue sample or organ sample derived therefrom, including, for example, cultured cell lines, biopsy, blood sample, or fluid sample containing a cell. For example, an organism may be an animal, including but not limited to, an animal such as a cow, a pig, a mouse, a rat, a chicken, a cat, a dog, etc., and is usually a mammal, such as a human.

As used herein, the term “Myc-driven tumor cell(s)” refers to a tumor cell(s) which has a genetic alteration which causes Myc overexpression, (c-Myc, MYCN, or LMYC), such as a genetic alteration which causes Myc overexpression as result of gene duplication, gene amplification, translocation, deregulated transcription leading to overexpression, or aberrant protein regulation. Examples of known genetic alterations which affect such dysregulation include a t8; 14 translocation, genetic amplification of c-Myc or other MYC-family member, and mutations in APC. Examples of Myc-driven tumor cells include Burkitts' Lymphoma cells, neuroblastoma cells, ovarian cancer cells, colon cancer cells, lung cancer cells, breast cancer cells, liver cancer cells, and others as shown in TABLE 1.

c-Myc is a key regulator of growth, proliferation, differentiation and development. Deregulation of the c-Myc oncoprotein has been reported in apoptosis, transformation, and in malignancies of lymphoid and non-lymphoid origin. The c-Myc gene encodes a transcription factor of the helix-loop-helix leucine zipper class and plays a role in the modulation and initiation of transcription. C-Myc binds to E-boxes (CACGTG) in the vicinity of target genes, which are then activated. The DNA binding activity requires dimerization with another helix-loop-helix leucine zipper protein called Max. Max can also interact with transcriptional repressors such as Mad and Mxil, which presumably down-regulate expression of c-Myc target genes. c-Myc is a short-lived nuclear oncoprotein, which is strictly regulated during the cell cycle of normal diploid cells. Increased half life of the protein is associated with immortalization and transformation. The deregulation of c-Myc is a common feature in many tumors, where it frequently is translocated and/or amplified and overexpressed. In addition, the c-myc gene is often the site of proviral insertion. See Marcu, et al., Cancer Research 56:36-39 (1992); Stanton et al., Mol. Cell. Biol. 14:5748-5755 (1983); and Cole et al., Ann. Rev. Biochem. 61:809 (1986).

N-Myc proto-oncogene protein, or MYCN or NMYC, is a protein encoded by the MYCN gene. As used herein, the terms “n-MYC”, “MYCN” and “NMYC” are synonyms and interchangeable. The gene is a member of the MYC family of transcription factors. The expressed protein contains a basic helix-loop-helix domain and must dimerize with another basic helix-loop-helix domain to bind DNA. Like c-Myc, the MYCN protein interacts with MAX. Amplification of the MYCN gene is mostly associated with a variety of tumors, most notably neuroblastomas.

The CSNK1 protein kinase family is evolutionarily conserved with seven mammalian isoforms: α, β, γ1, γ2, γ3, δ and ε. The human CSNK1ε protein (Genbank ref no. CAG30315.1) is set forth as SEQ ID NO:2, encoded by the cDNA (Genbank ref no. CR456429.1) set forth as SEQ ID NO:1. The terms casein kinase 1 epsilon, CSNK1 epsilon, CSNK1ε, and CSNK1ε are used interchangeably herein. The gene product of CSNK1ε is known to regulate circadian rhythms by phosphorylating other clock proteins, such as PERIOD. Over expression of CSNK1ε mimics WNT-signaling through phosphorylation of Tcf3 and stabilization of β-catenin, suggesting a functional role in stem cell properties. Additionally, the CSNK1ε protein phosphorylates p53 and prevents it from interaction with Mdm2. CSNK1ε is predominantly expressed in the neural system.

The present invention is based in part on the discovery that the c-isoform of casein kinase 1 (CSNK1ε) is upregulated in various Myc-driven cancers, and that inhibitors of CSNK1ε are effective in inhibiting the growth and/or proliferation of myc-driven cancer cells and reduce the size of established tumors, but do not adversely affect normally proliferating cells (i.e. not Myc-driven). As described below in Example 1, CSNK1ε expression was found to be elevated in neuroblastoma cells with amplified MYCN expression. Upon knockdown of CSNK1ε expression or chemical inhibition of CSNK1ε kinase activity, neuroblastoma cells with amplified MYCN expression exhibited a loss of viability and reduced proliferation. These results were replicated in vivo in a mouse xenograft model, as described in Example 2. First, xenograft neuroblastoma tumors containing inducible shRNAs targeting CSNK1ε exhibited a reduction in size upon induced knockdown of CSNK1ε expression. Second, administration of CSNK1ε small molecule inhibitor IC261 to mice with xenograft neuroblastoma tumors (with amplified MYCN expression) resulted in reduced tumor sizes. As further described herein, roles were discovered for WNT and SHH signaling in mediating the effect of CSNK1ε on tumor proliferation in neuroblastoma cells with amplified MYCN expression. A similar role for CSNK1ε expression was found in ovarian cancer cells with amplified c-MYC expression. As described in Example 4, ovarian cancer lines with amplified c-MYC expression also exhibited a reduction in viability and a reduction in WNT signaling upon induced knockdown of CSNK1ε expression. Administration of IC261 also reduced xenograft tumor cell viability in vivo and mouse survival times. An investigation of cell cycle checkpoints indicated that a majority of ovarian cancer cells with amplified c-MYC expression arrested at the G2 checkpoint of the cell cycle, but proceeded to replicate as they accumulated a greater than (>) G2 DNA content.

Inhibitors of CSNK1ε

In accordance with the foregoing, one aspect of the invention provides methods of screening for inhibitors of CSNK1ε and methods of using CSNK1ε inhibitors for inhibiting the growth and/or proliferation of a tumor comprising Myc-driven tumor cells comprising contacting the tumor cell with a CSNK1ε inhibitor. CSNK1ε inhibitors can reduce CSNK1ε kinase activity through a variety of mechanisms that are either direct or indirect. Accordingly, CSKNK1ε inhibitors can inhibit CSNK1ε at the DNA, mRNA, and polypeptide levels, targeting transcription, translation, and functional enzyme (kinase) activity.

In one embodiment, the inhibitor reduces the expression of CSNK1ε, thus reducing the levels of polypeptide product, i.e., the CSNK1ε kinase. For example, inhibition of expression can be performed by an agent that physically binds to the DNA encoding CSNK1ε, thus preventing access to the gene for transcription of the full length mRNA. Inhibition of transcription can also be accomplished, for example, by modification of the chromatin structure corresponding to the CSNK1ε gene locus.

In another embodiment, the inhibitory agent binds to or modifies the CSNK1ε mRNA molecules to prevent translation into the CSNK1ε kinase polypeptide. This can be accomplished, for example, using RNA interference. As described in Examples 1-4 below, inducible shRNA and siRNA were successfully employed to inhibit CSNK1ε expression.

In another embodiment, the CSNK1ε inhibitory agent inhibits CSNK1ε enzyme activity by binding to the CSNK1ε kinase domain or interfering with ability to bind or phosphorylate its substrate. Illustrative, non-limiting examples of such CSNK1ε inhibitory agents include small molecules, such as IC261, PF-4800567, and PF-670462. The structures of these inhibitors are illustrated below.

The CSNK1ε inhibitors identified by the method of the invention, as well as CSNK1ε inhibitors known in the art including IC261, PF-4800567, and PF-670462, can be used as therapeutic agents in the treatment of Myc-driven cancers in vivo and in vitro in accordance with the methods described herein.

In another aspect, the invention provides a method of screening for inhibitors of CSNK1ε. The method comprises contacting a Myc-driven tumor, cancer cell, or transformed cell, with a candidate CSNK1ε inhibitor agent. The Myc-driven cell is monitored for a reduction in CSNK1ε kinase activity or expression, wherein a resulting reduction in kinase activity or expression indicates that the candidate agent is an inhibitor of CSNK1ε.

In a preferred embodiment, the reduction in CSNK1ε kinase activity is determined by comparing the activity to a reference standard. In a further embodiment, the reference standard is a similar Myc-driven tumor, cancer, or transformed cell that is not contacted with the inhibitor agent. In another embodiment, the reference standard is the same Myc-driven tumor, cancer, or transformed cell before it is contacted with the inhibitor agent.

As described above, a person of skill in the art will understand that a reduction in CSNK1ε kinase activity or expression can be ascertained at the DNA, mRNA, and protein levels. Accordingly, in one embodiment, the reduction in CSNK1ε expression can be determined based on monitoring the transcriptional activity of the reduction in CSNK1ε, i.e., the relative abundance of RNA gene product. For example, commonly known methods can by applied to measure abundance of mRNA gene product, such as PCR, quantitative RT PCR. Another method is a nuclease protection assay, wherein an antisense probe (labeled with, e.g., radiolabeled or nonisotopic) hybridizes in solution to an RNA sample. Following hybridization, single-stranded, unhybridized probe and RNA are degraded by nucleases and intensity of antisense probe is determined for double stranded molecules. In yet another embodiment, Northern blot assays are used to detect and ascertain the relative amounts of RNA, such as mRNA, in a sample according to conventional Northern hybridization techniques known in the art.

In additional embodiments, RNA need not be extracted from the transformed cell or control cell. For example, fluorescent in situ hybridization can be used to determine the presence, relative quantity, and spatial distribution of target mRNA in a cell. In an illustrative example, Single Molecule RNA FISH (Biosearch Technologies, Novato, Calif.) uses multiple short singly labeled oligonucleotide probes complementary to distinct portions of the target sequence. When each probe binds to the single stranded mRNA template, it causes cooperative unwinding of the mRNA, promoting the binding of the additional probes. The net result is the binding of a large multitude of fluorescent labels to a single molecule of mRNA template, providing sufficient fluorescence to reliably locate each target mRNA in a wide-field fluorescent microscopy image.

Detectable probes, RNA interference molecules and the like useful for any of the methods described herein may be constructed according to well-known techniques based on the human cDNA sequence of the CSNK1ε gene (Genbank Ref No. CR456429.1), set forth as SEQ ID NO:1, or naturally occurring variants thereof.

In another embodiment, the reduction in CSNK1ε kinase activity can be determined based on monitoring the amount of the polypeptide CSNK1ε kinase in the sample. For example, immunoassays such as Western blot involve immunoprecipitation of protein from a sample according to methods well-known in the art. This is followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the protein sample. After separation of the proteins, immunocytochemistry and the like can by used to determine the amount of the CSNK1ε kinase present in the sample. A preferred agent for detecting a protein of interest is detectable antibody, or fragment thereof, capable of binding to the CSNK1ε kinase.

Antibodies can be generated utilizing standard techniques well known to those of skill in the art. Such antibodies can be polyclonal, or more preferably, monoclonal. An intact antibody, or an antibody fragment (e.g., Fab or F(ab′)₂), can be used. Detectable probes, such as antibodies and the like, useful for any of the methods described herein may be constructed according to well-known techniques utilizing polypeptide moieties containing aspects of the polypeptide sequence of the CSNK1ε kinase (Genbank Ref. No. CAG30315.1) (SEQ ID NO:2), or naturally occurring variants or derivatives thereof.

Additionally, antibodies, or fragments thereof can be employed histologically, as in immunofluorescence or immunoelectron microscopy, for in situ detection of CSNK1ε protein. In situ detection can be accomplished by obtaining a histological specimen (e.g., a biopsy specimen or immobilized cell culture) and applying thereto a labeled antibody that is directed to the CSNK1ε polypeptide. The antibody (or fragment) is preferably applied onto a biological sample. Through the use of such a procedure, it is possible to determine not only the presence of the protein of interest, but also its distribution within the sample. A wide variety of well-known histological methods (such as staining procedures) can be utilized in order to achieve such in situ detection.

Antibodies can be detected via direct labeling of the antibody via, e.g., coupling (i.e., physically linking) a detectable substance to the antibody, or indirect labeling of the antibody by reactivity with another reagent that is directly labeled. Examples of indirect labeling include detection of a primary antibody using a fluorescently labeled secondary antibody. In some embodiments, the biological sample can be brought in contact with and immobilized onto a solid phase support or carrier such as nitrocellulose, or other solid support which is capable of immobilizing cells, cell particles or soluble proteins.

The support can then be washed with suitable buffers followed by treatment with the detectably labeled fingerprint gene-specific antibody. The solid phase support can then be washed with the buffer a second time to remove unbound antibody. The amount of bound label on solid support can then be detected by conventional means. A wide variety of known signaling mechanisms are also available for the described immunoassays, such as fluorescein isothiocyanate, rhodamine, phycoerythrin, phycocyanin, allophycocyanin, o-phthaldehyde fluorescamine, and the like.

In another embodiment, the reduction in CSNK1ε kinase activity can be determined based on monitoring the enzymatic activity levels of the CSNK1ε kinase in a standard kinase assay. For example, small molecules such as IC261 may be screened in a kinase assay according to the methods described in Mashhoon M., et al., “Crystal Structure of a Conformation-selective Casein Kinase-1 Inhibitor,” The Journal of Biological Chemistry 275(26):20052-20060 (2000), hereby expressly incorporated by reference in its entirety. Briefly, standard activity assays for CSNK1ε kinase activity can be run at 37° C. The standard reaction (40 μl) contained 25 mM2-(N-morpholino)ethanesulfonic acid, pH 6.5, 50 mM NaCl, 15 mM MgCl₂, 2 mg/ml casein, 2 mM EGTA, 100 μM[γ-32P]ATP (100-400 cpm/pmol). Kinetic constants and their standard errors are calculated. For assay of inhibitor potency (IC₅₀), [γ-32P]ATP was held constant (10 μM), whereas of candidate inhibitor can be concentration was varied (such as 0.1, 0.3, 1, 3, and 10 μM). Assays contain 10 μM [γ-32P]ATP and variable concentrations of the candidate inhibitors. IC₅₀ values are calculated by known methods, for example, nonlinear regression algorithm of GRAPHPAD PRISM (GraphPad Software Inc.). Suitable synthetic or natural substrates containing a target amino acid sequence for measuring CSNK1ε kinase activity may also be utilized in a kinase assay.

Candidate compounds useful in the screening method include compounds from chemical libraries. Representative useful chemical libraries include libraries of structurally diverse compounds, libraries of therapeutic drug-like compounds, and libraries of therapeutic drugs approved by the Food and Drug Administration (FDA).

Myc-Driven Cancers

The normal Myc gene encodes a MYC transcription factor that has a role in the regulation of approximately 15% of all human genes. In addition to its role as a classical transcription factor, MYC is able to modify global chromatin structure by regulating histone acetylation. As described above, Myc-driven tumor cell(s) refers to a tumor cell(s) which has a genetic alteration which causes overexpression of a Myc oncogene. Such overexpression can be the result of a genetic alteration which causes deregulated mRNA expression of Myc, resulting in increased transcription rates. Moreover, overexpression can be the result of a translocation event in which the gene is adjacent to the Ig gene enhancer and therefore constitutively expressed in cells of B cell lineage, or there is a gene duplication, or amplification of the gene copy number (such as in neuroblastoma where hundreds of copies of MYCN gene are present). In such instances, the additional gene copies contribute to an increased expression signal, although any one gene locus might be regulated at a rate that would be considered normal. Nonlimiting examples of cancers exhibiting deregulated, thus over-expression of Myc are listed in Table 1.

TABLE 1 Illustrative human cancers with Myc Overexpression. Comment on Myc isotype and observed frequency Cancer type of Myc deregulation Neuroblastomas MYCN amplification in 30% Ovarian Cancer c-Myc amplification in 30-50% and overexpression in 60-70% Rhabdomyosarcoma MYCN amplification in 40-70% of alveolar type Rhabdomyosarcoma Liver Cancer c-Myc amplification in 30-50% and overexpression in 50-100% Melanoma c-Myc overexpression in 40-90% Breast Cancer c-Myc amplification in 20-50% of total, 90% in ductal type Colon Cancer c-Myc overexpression in 70% Prostate Cancer c-Myc amplification in 30-60% Burkitt's c-Myc translocation occur in all subtypes lymphomas Lung Cancer c-Myc, L-Myc and MYCN

In one embodiment of the method, the Myc-driven tumor cell is of neural origin. Cancers having neural origins include tumor cells derived from a primary neuroblastoma tumor, a metastatic neuroblastoma tumor or a brain tumor, which is caused by cancer of brain cells, metastatic brain cancer, which is cancer of another part of the body that has spread to the brain. Further examples of cancers of neural origin include, but not limited to: neuroblastoma; glioma (astrocytoma, glioblastoma, oligodendroglioma, schwannoma); medulloblastoma, also known as primitive neuroectodermal tumors (PNET); acoustic neuroma; pineocytoma and pineoblastoma; retinoblastoma; meningioma; ependymoma; brain stem gliomas; craniopharyngiomas; pineal region tumors neurocytomas; and ganglioneuromas.

A review of the body atlas of CSNK1ε expression demonstrated that the tissues with the highest expression are brain/fetal and pineal body. Additionally, among the 28 tissues of highest CSNK1ε expression, 15 are of neural origin, including brain/cerebellum, corpus callosum, thalamus, subthalamic nucleus, pons, amygdaloid body, hypothalamus, frontal lobe, prefrontal cortex, dorsal root ganglia, and caudate nucleus. Additionally, reference to the Oncogenomics Database indicated that CSNK1ε is highly expressed in clinical samples of neuroblastoma cells that exhibit aberrant or high levels of n-MYC expression.

In another embodiment, the Myc-driven cancer is an ovarian cancer. In another embodiment, the Myc-driven cancer is selected from the group consisting of rhabdomyosarcoma, liver cancer, melanoma, breast cancer, colon cancer, prostate cancer, Burkitt's lymphoma and lung cancer.

In one aspect, the present invention provides methods for inhibiting the growth and/or proliferation of Myc-driven tumor cells comprising contacting the cells with a CSNK1ε inhibitor. In one embodiment, the tumor cell is contacted in vitro. In another embodiment, the tumor cell is contacted in vivo in a mammalian subject. In some embodiments, the mammalian subject is a primate, rodent, canine, feline, horse or cow.

In preferred embodiments, the mammalian subject is a human. In one embodiment, the CSNK1ε inhibitor is a small molecule. In some embodiments small molecule inhibitor of CSNK1ε is at least one of IC261, PF-4800567 or PF-670462.

In another aspect, the invention provides a method of treating a subject suffering from a tumor comprising myc-driven tumor cells, comprising administering to the subject an amount of a composition comprising a CSNK1ε inhibitor effective to inhibit the growth and/or proliferation of the tumor cells. Examples of Myc-driven cancers are described herein. In some embodiments, the subject is suffering from a myc-driven cancer of neural origin, examples of which are provided herein. In some embodiments, the myc-driven tumor cell of neural origin is derived from a primary neuroblastoma tumor, a metastatic neuroblastoma tumor or a brain tumor. In some embodiments, the subject is suffering from an ovarian cancer comprising myc-driven tumor cells. In some embodiments, the subject is suffering from a cancer comprising myc-driven tumor cells selected from the group consisting of rhabdomyosarcoma, liver cancer, melanoma, breast cancer, colon cancer, prostate cancer, Burkitt's lymphoma and lung cancer.

In some embodiments, the method further comprises the step of determining whether the tumor in said subject comprises myc-driven tumor cells prior to treatment with said composition comprising a CSNK1ε inhibitor. The step of determining whether the tumor in said subject comprises myc-driven tumor cells may be carried out by accessing a database, or by assaying cells obtaining from the subject (such as a biopsy sample from said subject) for an aberrantly high level of Myc protein or mRNA expression as compared to normal cells (or as compared to a reference standard), or by assaying cells obtained from the subject for the presence of amplified gene copies of cDNA encoding Myc, using standard methods known in the art and as further described herein.

In some embodiments, the composition comprising a CSNK1ε inhibitor is effective to selectively inhibit the growth and/or proliferation of the myc-driven tumor cells, while not inhibiting the growth and proliferation of non-myc driven cells (i.e. cells with normal, low levels of myc).

Administration of the composition comprising a CSNK1ε inhibitor effective to inhibit the growth and/or proliferation of the myc-driven tumor cells can be performed according to a variety of well-known methods, which can include steps for inhibiting tumor cells including providing the inhibitor in a pharmaceutical carrier, methods of administration to a cell in vitro (in cell culture), or administration to a mammalian subject in vivo by any mode known in the art which retains agent activity and provides access to the cancer cells. These include, without limitation, oral, intravenous, intraperitoneal, subcutaneous, intramuscular, and intrathecal routes of administration.

Pharmaceutical compositions comprising CSNK1ε inhibitors are also provided. Such a composition contains from about 0.01 to 90% by weight (such as 1 to 20% or 1 to 10%) of the CSNK1ε inhibitor in a pharmaceutically acceptable carrier. Solid formulations of the compositions for oral administration may contain suitable carriers or excipients, such as corn starch, gelatin, lactose, acacia, sucrose, microcrystalline cellulose, kaolin, mannitol, dicalcium phosphate, calcium carbonate, sodium chloride, or alginic acid. Liquid formulations of the compositions for oral administration prepared in water or other aqueous vehicles may contain various suspending agents such as methylcellulose, alginate, tragacanth, pectin, kelgin, carageenan, acacia, polyvinylpyrrolidone, and polyvinyl alcohol.

Injectable formulations of the compositions comprising a CSNK1ε inhibitor may contain various carriers such as vegetable oils, dimethylacetamide, dimethylformamide, ethyl lactate, ethyl carbonate, isopropyl myristate, ethanol, or polyols (glycerol, propylene glycol, liquid polyethylene glycol and the like). For intravenous injections, water soluble versions of the compounds may be administered by the drip method, whereby a pharmaceutical formulation containing an antifungal agent and a physiologically acceptable excipient is infused. Physiologically acceptable excipients may include, for example, 5% dextrose, 0.9% saline, Ringer's solution, or other suitable excipients. Intramuscular preparations, e.g., a sterile formulation of the compounds of the invention, can be dissolved and administered in a pharmaceutical excipient such as water-for-injection, 0.9% saline, or 5% glucose solution.

Conventional methods, known to those of ordinary skill in the art of medicine, can be used to administer the pharmaceutical formulations to a mammalian subject. The pharmaceutical formulations can be administered via oral, subcutaneous, intrapulmonary, transmucosal, intraperitoneal, intrauterine, sublingual, intrathecal, intramuscular, nasal, rectal, vaginal, and other routes of delivery that effectively result in dispersion of the delivered agent to a single or multiple sites of intended therapeutic action.

The compositions comprising a CSNK1ε inhibitor in accordance with the invention may be systemically or locally administered on a periodic basis at intervals determined to maintain a desired level of therapeutic effect. For example, a composition comprising a CSNK1ε inhibitor may be administered, such as by subcutaneous injection, daily, weekly, every two to four weeks or at greater or less frequent intervals. The dosage regimen will be determined by the physician considering various factors that may influence the action of the combination of agents. These factors will include the extent of progress of the condition being treated, the patient's age, sex and weight, and other clinical factors. The dosage for each individual agent will vary as a function of the inhibitory agent that is included in the composition, as well as the presence and nature of any drug delivery vehicle (e.g., a sustained release delivery vehicle).

In some embodiments of the method, the subject suffering from a tumor comprising myc-driven tumor cells is further provided with one or more additional anti-cancer therapies. The additional therapies can include surgery, chemotherapy using chemical therapeutic agents distinct from the CSNK1ε inhibitor, and radiation therapy. In some embodiments, the additional therapies include administration of an inhibitor of SHH expression or activity and/or an inhibitor of WNT expression or activity.

In one embodiment, the myc-driven tumor cell exhibits resistance, or some level of reduced sensitivity to the additional chemotherapeutic agent, and the administration of the additional chemotherapeutic agent with the CSNK1ε inhibitor renders the tumor cells susceptible to the additional chemotherapeutic agent. In one embodiment, the myc-driven tumor comprises cells that are resistant to cisplatin and the CSNK1ε inhibitor renders the cells susceptible to cisplatin. Accordingly, in some embodiments, the composition containing the CSNK1ε inhibitor is administered to a subject undergoing treatment with cisplatin. In one embodiment, the invention provides a composition comprising a CSNK1ε inhibitor in combination with a chemotherapeutic agent, such as Cisplatin.

In another aspect, the invention provides a method for identifying compounds capable of inhibiting proliferation of a myc-driven cancer cell. The method comprises contacting a myc-driven cancer cell line expressing CSNK1ε with a candidate compound in cell culture. Then a determination is made of at least one of: (i) the level of WNT expression or activity in the presence and absence of the candidate compound, (ii) the level of SHH expression or activity in the presence and absence of the candidate compound, or (iii) the level of CSNK1ε expression or activity in the presence and absence of the candidate compound. A decrease in the expression level or activity of WNT; and/or a decrease in the expression level or activity of SHH, and/or a decrease in the expression level or activity of CSNK1ε in the presence of the candidate compound is indicative of a compound that inhibits proliferation of a cancer cell.

Detection of WNT, SHH or CSNK1ε expression or activity can be performed by methods well known in the art. For example, methods for detection of mRNA and polypeptide gene products to indicate expression levels are described above. Additionally, detection of signaling activity can be performed using well-known reporter assays. For example, as described in Example 3 and 4, a WNT dual reporter system employing consensus (TOP) and mutant (FOP) TCF binding sites to assay the β-catenin activity. β-catenin activity is a functional reporter of WNT signaling, and therefore, its detection according to this methods permits the measurement of WNT signaling in response to experimental systems. Additionally, a similar dual reporter SHH system is described in Example 3 utilizing Gli detectable reporters to permit the assaying of SHH signaling. Accordingly, in further embodiments, the method comprises a tumor cell line comprising a gene operationally linked to WNT. In another embodiment, the method comprises a tumor cell line comprising a gene operationally linked to SHH.

In some embodiments, the myc-driven cancer cell line expressing CSNK1ε is a neuroblastoma cell or an ovarian cancer cell. In some embodiments, the cancer cell line comprises a reporter gene operationally linked to WNT. In some embodiments, the candidate compound is from a library of structurally diverse compounds, a library of therapeutic drug-like compounds, or a library of therapeutic drugs approved by the Food and Drug Administration (FDA).

The following examples merely illustrate the best mode now contemplated for practicing the invention, but should not be construed to limit the invention. All literature citations are expressly incorporated by reference.

Example 1

This Examples describes the use of inhibitors of CSKN1ε to inhibit proliferation of neuroblastoma cells in vitro.

Rationale

In an siRNA screen in human fibroblast derived cells, it was determined that short hairpin RNAs (shRNAs) targeting CSNK1ε induced growth inhibition in these engineered cells (Yang, W. S., and B. R. Stockwell, “Inhibition of Casein Kinase 1-epsilon Induces Cancer-Cell-Selective, PERIOD2-Dependent Growth Arrest,” Genome Biology 9:R92, 2008). An examination of the CSNK1ε gene sequence revealed several putative MYC-MAX binding sites in the promoter regions around Exon 1. Neuroblastoma is a pediatric cancer that often presents with amplification MYCN, the neuronal expressed homologue of c-MYC, for review see Park, J., et al., “Neuroblastoma: Biology, Prognosis and Treatment,” Pediatric Clinics of North America 55:97-120, 2008. MYCN is a well-documented driver of neuroblastoma initiation and maintenance in mouse models (Weiss, W. A., et al., “Targeted Expression of MYCN Causes Neuroblastoma in Transgenic Mice,” Embo J 16:2985-2995, 1997) and the strongest molecular marker of poor prognosis (Riley, R. D., et al., “A Systematic Review of Molecular and Biological Tumor Markers in Neuroblastoma,” Clin Cancer Res 10:4-12, 2004). This hypothesis stems from the shared c-MYC and MYCN transcriptional programs and cellular phenotypes (Boon, K., et al., “N-myc Enhances the Expression of a Large Set of Genes Functioning in Ribosome Biogenesis and Protein Synthesis,” EMBO J 20:1383-1393, 2001; Mestdagh, P., et al., “MYCN/c-MYC-Induced microRNAs Repress Coding Gene Networks Associated With Poor Outcome in MYCN/c-MYC-Activated Tumors,” Oncogene 29:1394-1404) and by the observation that c-MYC can functionally replace MYCN during murine development (Malynn, B. A., et al., “N-myc Can Functionally Replace c-myc in Murine Development, Cellular Growth, and Differentiation,” Genes Dev 14:1390-1399, 2000). Additionally, reference to microarray data available at Oncogenomics neuroblastoma prognosis database indicated that survival of neuroblastoma segregated on the basis of CSNK1ε expression. Specifically, neuroblastoma patients with high CSNK1ε had significantly shorter survival than patients with low CSNK1ε.

Therefore, the inventors investigated CSNK1ε as a novel therapeutic target for cancers of neural origin, specifically in neuroblastoma cells, as described below.

Methods and Results

CSNK1ε Expression is Elevated in Neuroblastoma Cells with High MYCN Expression.

An examination of the CSNK1ε gene sequence revealed several putative MYC-MAX binding sites in the promoter regions around Exon 1. This observation indicated that CSNK1ε is a potential transcriptional target of MYC. This hypothesis was further supported by the observation that CSNK1ε was induced in a transgenic neuroblastoma cell line containing a tetracycline-inducible vector encoding MYCN (data not shown).

In order to determine whether a correlation exists between high MYCN levels and CSNK1ε expression, CSNK1ε and MYCN protein levels were assayed by Western Blot from three different neuroblastoma cell lines: SK-N-AS, SK-N-BE2 and IMR-32. Protein was extracted from cell lysates of SK-N-AS, SK-N-BE2 and IMR-32 neuroblastoma cell lines using standard protein isolation techniques known in the art. The extraction samples were separated by SDS-PAGE electrophoresis and blotted according to standard protocols with the following antibodies: anti-CSNK1e (610445, BD Biosciences), anti-n-Myc (NCM-II, Santa Cruz Biotechnology), and anti-Actin (AC-15, abcam, Cambridge, UK). Quantitation of the Western blot was performed using ImageJ software (NIH).

As illustrated in FIG. 1A, dense bands indicating high levels of CSNK1ε protein product were detected in neuroblastoma cells lines SK-N-BE2 and IMR-32, which also displayed overexpression of MYCN. In contrast, SK-N-AS neuroblastoma cells had minimal CSNK1ε protein product and no detectable MYCN protein product. An expanded Western Blot analysis incorporating five additional neuroblastoma cell lines (SH-SY-5Y, NBL-W-N, KCN, KCNR, and LA-N-5) was also conducted. Polypeptide levels were detected using antibodies specific for MYCN, MYC (polyclonal), CSNK1ε, and Actin. Comparison of CSNK1ε/Actin expression to MYCN/Actin expression revealed a positive correlation (R2=0.639; p-0.038) between CSNK1ε and MYCN expression in the neuroblastoma cells.

The positive correlation between CSNK1ε and MYCN expression was also confirmed at the transcriptional level. RNA was extracted from cultures of SK-N-AS, SK-N-BE2 and IMR-32 neuroblastoma cell lines according to standard protocols. mRNA corresponding to CSNK1ε was reverse transcribed and amplified using quantitative RT PCR using standard cycling parameters. As illustrated in FIG. 1B, between 4 and 5-fold more CSNK1ε mRNA was detected by qRTPCR in the neuroblastoma cell lines, SK-N-BE2 and IMR-32, known to over-express n-MYC, as compared to a control neuroblastoma line, SK-N-AS, which does not over express n-MYC.

There are six different isoforms of CSNK1, which are encoded by separate genes (Hanks, S. K., and T. Hunter, T., “Protein Kinases 6: The Eukaryotic Protein Kinase Superfamily: Kinase (Catalytic) Domain Structure and Classification,” Faseb J 9:576-596, 1995). In order to analyze the role of Myc in the regulation of the CSNK1ε gene, MYCN expression and CSNK1ε expression was investigated for all CSNK1 isotypes to determine if there was a correlation. Neuroblastoma cells with different MYCN expression levels were analyzed by qRT-PCR to determine the expression pattern of different CSNK1 isoforms and any correlation with amplified MYCN expression. Seven neuroblastoma cell lines were used. The neuroblastoma lines SK-N-AS and SH-SY-5Y have low, or non-amplified MYCN expression, whereas the neuroblastoma lines LAN-5, IMR-32, KCN, KCNR, and SK-N-BE2 have amplified MYCN expression. As illustrated in FIG. 2, the epsilon isoform was the predominant isoform of CSNK1 expressed in neuroblastoma cell lines that also had amplified MYCN expression. Therefore, the correlation and functional relationship between MYCN and CSNK1ε expression appeared to be specific for the epsilon isoform of CSNK1.

Taken together, these data indicate that CSNK1ε expression correlates with the high expression of the MYCN oncogene in multiple, high MYCN expressing neuroblastoma cell lines. Furthermore, MYCN appears to directly regulate transcription of the CSNK1ε gene. This indicates that CSNK1ε is important for the viability of cells with amplified MYCN expression, thereby making CSNK1ε a potential therapeutic target in Myc-driven cancer cells of neural origin.

Knock-Down of CSNK1 Expression Reduced Viability of Cells with Amplified MYCN Expression.

To test the effect of CSNK1ε inhibition on the growth of neuroblastoma cell lines, lentiviral vectors were constructed that enable the conditional knock-down of CSNK1ε upon induction by doxycycline (“Dox”), a semi-synthetic tetracycline compound. SK-N-BE2 neuroblastoma cells (with MYCN gene amplification) were transfected with a control shRNA construct, and the following two shRNA constructs corresponding to two different target sequences of the CSNK1ε mRNA sequence. The two core target sequences of CSNK1e used in the dox inducible shRNA are listed below:

(SEQ ID NO: 3) CSNK1e sh#1 (GGCTATCCCTCCGAATTCT) (SEQ ID NO: 4) CSNK1e sh#2 (GAACGGATCAGCGAGAAGA)

The shRNA encoding plasmids were transfected into the cells and were cultured in the presence or absence of Dox for 4 days before gene expression levels were quantified with qPCR. FIG. 3A illustrates that the relative expression of CSNK1ε fell to between about 0.4 and about 0.6 of normal levels upon Dox-induced expression of the first and second shRNA constructs corresponding to CSNK1ε, respectively. This was confirmed at the protein level by Western blot analysis where the measurable protein levels of CSNK1ε gene product were reduced in transfected cells treated with Dox. See FIG. 3B. This demonstrates the effectiveness of the inducible lentivirus vector encoding CSNK1ε siRNAs to knockdown expression of the CSNK1ε gene and the corresponding polypeptide gene product. Notably, the knock-down of CSNK1ε did not affect expression of the other isoforms, as determined by qPCR, indicating the specificity of the shRNA targeting hairpin (data not shown).

Lentiviral vectors expressing Dox-inducible shRNAs targeting CSNK1ε were transduced into SK-N-AS, a neuroblastoma line with normal MYCN expression, and SK-N-BE2 and IMR-32, neuroblastoma lines with amplified MYCN expression. Expression of the shRNAs were induced with Dox and cell viability was assayed after four days using the CellTiter Glo assay (Promega, Madison, Wis.). As illustrated in FIG. 3C, induction of both CSNK1ε shRNA constructs caused a substantial loss of cell viability in the neuroblastoma cells lines with amplified MYCN (SK-N-BE and IMR32), but not in neuroblastoma cells with normal MYCN expression (SK-N-AS). This demonstrates that expression of CSNK1ε is required only in the context of aberrant, enhanced expression of the MYC oncogene in neuroblastoma cells.

Additionally, the effects of CSNK1ε or MYCN transient knock-down upon cell viability were assessed in SK-N-AS and IMR-32 cells. The cells were transfected with siRNAs pools (three different duplexes) specific for each gene. At 96 hours post-transfection, viability of the cells was measured by CellTiter-Glo assay (Promega, Madison, Wis.). As illustrated in FIG. 3D, the transient knockdown of both CSNK1ε and MYCN resulted in a significantly greater reduction in the cell viability in the neuroblastoma cells with amplified MYCN (SK-N-BE) as compared to the neuroblastoma cells with normal MYCN expression (SK-N-AS). The data shown in FIG. 3D represents the mean viability±SD relative to cells transduced with a control constructs.

Chemical Inhibition of CSNK1 Kinase Activity Blocks Growth of Neuroblastoma.

To evaluate the therapeutic potential of CSNK1ε kinase inhibitors for the inhibition of tumor cell growth, the kinase function of CSNK1ε polypeptide was blocked with IC261, a small molecule inhibitor of CSNK1ε and d kinase activity (Mashhoon, N., et al., “Crystal Structure of a Conformation-Selective Casein Kinase-1 Inhibitor,” J Biol Chem 275:20052-20060, 2000). Specifically, the sensitivity of MYC overexpressing cells to IC261 relative to control, was determined in vitro utilizing the neuroblastoma cell lines SK-N-AS (normal MYCN expression) and IMR-32 (amplified MYCN expression). Cultured cells were treated with a range of concentrations of IC261 and percent of cell viability was recorded over four days as described above. After only 48 hours with IC261 concentrations of 0.33 μg/ml and higher, IMR-32 neuroblastoma cells (amplified MYCN expression) exhibited a lower percent cell viability compared to SN-N-AS neuroblastoma cells (normal MYCN expression). The difference in cell viability was significant at the 1, and 10 μM concentrations. See FIG. 4A. The significant difference in cell viability between the neuroblastoma cell lines persisted to 72 hours. See FIG. 4B. The difference between viability of neuroblastoma cells lines persisted even to 96 hours at the higher doses (but the difference was not statistically significant). See FIG. 4C.

Microscopic analysis of the SN-N-AS (normal MYCN expression) and IMR-32 (amplified MYCN expression) neuroblastoma cell lines, further supporting the differential effect of the CSNK1ε inhibitor, IC261, on the health and proliferation of neuroblastoma cells overexpressing MYCN. Referring to FIG. 5, top line, micrographs are provided illustrating SK-N-AS (normal MYCN expression) cells in culture before and 48 hours after culture with DMSO, 0.33 μM, or 3.3 μM IC261. Referring to FIG. 5, bottom line, micrographs are provided illustrating IMR-32 cells (amplified MYCN expression) in culture before and 48 hours after culture with DMSO, 0.1 μM, or 1.0 μM IC261. Pre-treatment cells and DMSO-treated cells from both lines exhibited healthy spreading. However, after 48 hours of treatment of IC261, the majority of IMR-32 blastoma cells appeared to have detached from the plate surface and balled up, whereas a large proportion of the SN-N-AS maintained healthy spreading and attachment. These results demonstrate that CSNK1ε function is not required for growth and proliferation of cells with normal MYCN levels, however, CSNK1ε is required for growth and proliferation of cells with aberrantly high expression of MYCN (i.e., amplified MYCN).

Conclusion

These data demonstrate that expression of CSNK1ε is elevated in neuroblastoma cells with amplified expression of MYCN. Further, these results demonstrate that MYCN directly regulates the transcription of CSNK1ε. Moreover, these results demonstrate that knockdown of CSNK1ε expression, or chemical inhibition of the CSNK1ε kinase function specifically reduces the viability of neuroblastoma cells with amplified MYCN levels, but does not inhibit viability of cells with normal MYCN levels. Thus, CSNK1ε is only required in the context of aberrant, enhanced expression of the MYC oncogene in neuroblastoma cells. These results establish CSNK1ε as a viable therapeutic target for inhibiting growth and/or proliferation of MYC-driven tumor cells.

Example 2

This Example demonstrates the use of inhibitors of CSKN1ε to inhibit proliferation of neuroblastoma cells in vivo in a mouse xenograft model.

Rationale

As described in Example 1, CSNK1ε expression was found to be associated with elevated MYCN expression in neuroblastoma cells. Additionally, CSNK1ε expression and kinase function was found to be required for continued viability of neuroblastoma cells with aberrantly high MYCN expression. Therefore, inhibition of CSNK1ε in established tumors with high MYCN expression was investigated in vivo.

Methods and Results

Knock-Down and Chemical Inhibition of CSNK1 Kinase Activity Blocks Growth of Neuroblastoma Xenografts.

The efficacy of CSNK1ε knock-down (expression and functional knockdown) in the inhibition of tumor growth in vivo was tested in a therapeutic model of neuroblastoma xenograft mice using the SK-N-BE2 and IMR-32 cell lines, respectively.

To establish the viability of CSNK1ε as target for cancer therapeutics, expression of CSNK1ε was knocked down using inducible shRNA interference in established SK-N-BE2 (amplified MYCN expression) xenograft blastoma tumors. Specifically, SK-N-BE2 cells were transduced in vitro with Dox-inducible lentivirus vectors encoding shRNA targeting the CSNK1ε mRNA or a control, as described above in Example 1, and injected into mice as follows. Approximately 2×10⁶ cells were subcutaneously injected in the flank of NOD/SCID mice. The resulting engrafted tumors were permitted to establish for 2-3 weeks. The mice were then injected daily for seven days with 1 mg/ml Dox in 5% sucrose water. As illustrated in FIGS. 6A-D, three out of four mice with tumors containing the shCSNK1ε vectors exhibited inhibition of tumor growth upon Dox induction, indicating that silencing of CSNK1ε was effective in blocking growth of neuroblastoma cells with aberrantly high MYCN expression.

To evaluate the therapeutic potential of CSNK1ε kinase inhibitors, IC261, a small molecule inhibitor of CSNK1ε and d kinase activity (Mashhoon, N., et al., “Crystal Structure of a Conformation-Selective Casein Kinase-1 Inhibitor,” J Biol Chem 275:20052-20060, 2000) was administered to mice with established IMR-32 (amplified MYCN expression) xenograft blastoma tumors. Specifically, 10 NOD/SCID mice were injected with 1×10⁷ IMR-32 blastoma cells. The tumors were allowed to establish for 6 weeks. The mice were randomized into control and IC261 treatment groups. At the start of treatment, the average tumor size for the control mice was 98.8±42.5 mm³, whereas the average tumor size for the IC261 treatment group was 121.9±46.9 mm³. The groups were subcutaneously injected once daily for seven days with 20.5 mg/kg of IC261 or DMSO in 200 μl. During treatment, the tumor size was monitored. As illustrated in FIG. 7A, during the first two days of treatment, there was no significant difference in tumor volume between the DMSO and IC261-treated mice. However, at day three the average tumor volume of the IC261-treated mice was reduced, a trend that continued throughout the remaining treatment schedule, ultimately to a volume of about 100 mm³. In contrast, the tumor volume of the DMSO-treated mice continued to increase to a volume of about 350 mm³. Photographs of a representative mouse from the IC261 and control groups, before and after treatment, are shown in FIGS. 7B and C, respectively. Histological sections of tumors from each group were prepared after the 8th day of IC261 treatment. The tumor sections were subjected to hematoxylin and eosin (H-E) stain, TUNEL stain, and BrdU staining to ascertain the cell structure, and frequencies of cell apoptosis, and cell proliferation within the tumors. As shown in FIG. 7D, the IC261-treated tumor has drastically reduced indications of cell proliferation in the BrdU stain in comparison to the control (DMSO-treated) tumor. The images shown in FIG. 7D are representative of at least 10 fields viewed over two stained sections per animal.

Conclusion

This Example demonstrates that the reduction of CSNK1ε expression and/or enzymatic activity, whether by expression knockdown or chemical inhibitor of the kinase domain, was effective to inhibit the growth and proliferation of cancer cells and reduced the tumor size of MYC-driven neuroblastoma cancers. These results validate CSNK1ε as a therapeutic target for MYC-driven cancers.

Example 3

This Example describes a method for determining the functional status of WNT activity in neuroblastoma cells, and methods for screening for inhibitors of CSNK1ε.

Rationale

As described in Example 1, high expression of CSNK1ε was found to correspond with amplified expression of MYC oncogene in tumor cells and selective inhibition of CSNK1ε expression or kinase activity was found to result in reduced viability of neuroblastoma cells with amplified MYCN expression. Further, as described in Example 2, selective inhibition of CSNK1ε expression or kinase activity in neuroblastoma xenografts with amplified MCYN expression was found to result in a reduction in tumor size in vivo. To better understand the functional mechanisms that drive the relationship between CSNK1ε and MYC oncogenes, the role of CSNK1ε in two developmental pathways was investigated with reference to MYC expression.

Methods and Results

CSNK1 Knock-Down Influences Two Developmental Pathways, WNT and SHH.

CSNK1ε has been implicated as a positive regulator of WNT signaling (Sakanaka, C., “Phosphorylation and Regulation of Beta-Catenin by Casein Kinase I Epsilon,” J Biochem 132:697-703, 2002). To determine the functional status of WNT activity in neuroblastoma cells with or without amplified MYCN expression, a WNT dual reporter system, employing both consensus (TOP) and mutant (FOP) TCF binding sites was assayed in neuroblastoma cell lines SK-N-AS (MYCN not amplified), SH-Sy5Y (MYCN not amplified), IMR-32 (MYCN amplified and overexpressed), and SK-N-BE2 (MYCN amplified and overexpressed), as described in (Biechele, T. L., et al., “Transcription-Based Reporters of Wnt/beta-Catenin Signaling,” Cold Spring Harb Protoc 2009, pdb prot5223). As illustrated in FIG. 8A, WNT mediated transcriptional response was markedly elevated in cells with MYCN amplification, (i.e., IMR-32 and SK-N-BE4), as indicated by β-catenin signaling.

A potential direct connection of WNT with MYCN expression was explored utilizing neuroblastoma cells expressing an inducible Tet-MYCN gene. Tet-21N neuroblastoma cells (normal MYCN expression) carrying a Tet-off-MYCN gene, were treated with or without Dox (a tetracycline compound), as described supra. Western blot analysis indicated that Tet-MYCN cells receiving Dox lowered CSNK1ε expression in parallel with repression of the levels of MYCN as compared to the no-Dox cells (data not shown). Further, the WNT activity was assayed through the detectable activity of an integrated WNT reporter. As illustrated in FIG. 8B, the neuroblastoma cells with MYCN-on expression had highly elevated WNT signaling, as indicated by detectable β-catenin signal and the addition of IC-261 resulted in the repression of the WNT reporter. These results suggest that MYCN may exert a positive feedback on WNT in neuroblastoma, which is consistent with the previous report that c-MYC overexpression positively affects WNT in breast cancer cells (Cowling, V. H., and M. D. Cole, “Turning the Tables: Myc Activates Wnt in Breast Cancer,” Cell Cycle 6:2625-2627, 2007).

The conditional knock-down of CSNK1ε using the Dox-inducible lentiviral constructs described supra also lowered the activity of an integrated WNT reporter in neuroblastoma cells (data not shown). This indicates that CSNK1ε activity mediates the MYCN effect on WNT signaling activity.

However, it is noted that knock-down of a key mediator of WNT signaling, β-catenin, using a siRNA construct (“siCTNNB1”) had equivalent affects on the viability of SK-N-AS and SK-N-BE2, neuroblastoma lines with non-amplified MYCN and amplified MYCN, respectively. See FIG. 8C. These results suggested that the selective growth inhibition caused by CSNK1ε knockdown may be caused by both WNT-dependent and independent effects.

To delineate at a global level the effects of CSNK1ε knock-down, microarray analysis of mRNA isolated after conditional silencing of CSNK1ε was carried out in SK-N-BE2 neuroblastoma cells (MYCN amplified and overexpressed) and compared with samples transduced with a control lentiviral vector. The results indicated significant changes in gene expression of a broad set of genes. Pathway analysis of the down-regulated genes revealed that several were implicated in Sonic Hedgehog (“SHH”) signaling. This indicated that the SHH developmental pathway plays a role in the cellular response to CSNK1ε knock-down. To verify SHH involvement in neuroblastomas with MYCN amplification, a GLI dual reporter system was assayed in neuroblastoma cell lines according to the method previously described in Sasaki, H., et al., “A Binding Site for Gli Proteins Is Essential for HNF-3beta Floor Plate Enhancer Activity in Transgenics and Can Respond to Shh in vitro,” Development 124:1313-1322, 1997. GLI1 is the downstream transcription factor that mediates SHH response and reporters carrying GLI1 binding sites are utilized to measure the status of the pathway. As illustrated in FIG. 8D, high Gli/mGli ratios were observed in IMR-32 and SK-N-BE2 neuroblastoma lines (both with amplified MYCN expression) versus SK-N-AS and SH-SY5Y neuroblastoma lines (both with normal MYCN expression), indicating high SSH reporter levels in the neuroblastomas with amplified MYCN expression.

Cyclopamine, a known natural inhibitor of SHH, was administered to SK-N-AS and IMR-32, to assess the impact of SHH inhibition on cell viability of neuroblastoma cells with normal and amplified MYCN expression, respectively. Cyclopamine was administered to the SK-N-AS and IMR-32 in 1 μM or 10 μM doses, and the growth inhibition was assayed at 48, 72 and 96 hours. Growth inhibition was detected in both neuroblastoma cell types. However, the effect was more pronounced in neuroblastoma cells with amplified MYCN expression (IMR-32). See FIGS. 8E and F. Combined, these data indicate a dependence of MYC overexpressing cells on a functional SHH signaling pathway and its interaction with CSNK1ε function.

Conclusion

These results indicate that CSNK1ε influences both WNT and SHH signaling through a potential positive feedback loop set up by MYCN amplification. The activity of both pathways appears to contribute to the proliferative potential neuroblastomas that overexpress of MYCN.

Example 4

This Example demonstrates the use of inhibitors of CSKN1ε to inhibit proliferation of ovarian cancer cells in vitro and in vivo.

Rationale

As described in Examples 1-2, elevated expression of CSNK1ε was found to correlate with amplified expression of MYCN in neural cancer cells. As demonstrated in Example 1 and 2, reduction of CSNK1ε in cancer cells with amplified MYCN expression reduced the viability of the cells, both in vitro and in vivo. Further, as described in Example 3, the proliferative effects of CSNK1ε on neuroblastoma cells with amplified MYCN expression are likely mediated by WNT and SHH signaling, which provides a positive feedback on the regulation of CSNK1ε. To assess whether CSNK1ε plays a similar role for other isotypes of MYC in non-neural cancers, expression of CSNK1ε was manipulated in ovarian cancer cells that exhibited amplified MYC expression.

Methods and Results

Characterization of ovarian cancer lines for c-MYC expression status.

Six human ovarian cancer cell lines were characterized for their relative expression levels of c-MYC as follows. First, a Western blot was performed using protein extractions obtained from the ovarian cancer cell lines CaOV3, RMG-1, DOV-13, PE04, IGROV-1, and TOV112D. The protein extractions were separated by SDS-PAGE, blotted and probed with a c-MYC monoclonal antibody (sc-42 and sc-764, Santa Cruz Biotechnology) under stringent hybridization conditions.

As illustrated in FIG. 9A, the Western blot revealed high levels of cMYC in PE04, and especially in IGROV-1 and TOV112D cell lines. In contrast, the Western blot revealed low c-MYC levels in CaOV3 cells, and no detectable c-MYC in RMG-1 and DOV-13 ovarian cancer cell lines. As a control, human foreskin primary cells (HFF with control vector pBabe) that express low levels of c-MYC were used as a negative control, and HFF cells with a c-MYC transgene was used as a positive control.

Second, c-MYC mRNA was quantified in various ovarian cancer cell lines using quantitative RT-PCR. The expression levels of c-MYC were normalized to the detected levels of the reference standard gene, GAPDH. FIG. 9B illustrates the normalized c-MYC mRNA levels in increasing order. Spotted bars indicate cell lines with an approximate single gene copy of GAPDH, whereas open boxes represent cell lines with multiple gene copies of the standard gene. It is noted that the cell lines PE04, IGTOV-1 and TOV112D, previously identified by the Western blot assay as having elevated levels of c-MYC polypeptide, are among the ovarian cell lines with the highest mRNA levels for c-MYC.

Third, because many transformed cells exhibiting MYC-driven overexpression and therefore MYC-driven proliferation are known to have experienced duplications in the MYC gene, the copy number of c-MYC was assessed by PCR in the ovarian cancer cell lines. The copy number of the various assayed ovarian cancer cell lines are represented in FIG. 9C as a function of GAPDH copy number. It is noted that IGROV-1 and PE04, which were previously identified as having amplified c-MYC expression have increased copy numbers of the c-MYC gene. The TOV112D cell line, however, does not appear to have increased c-MYC copies, which indicates that the amplified expression levels of the gene in these cells results from de-regulated transcription from a single gene locus.

Knockdown of CSNK1 Expression in Ovarian Cancer Cells with Amplified c-MYC.

siRNAs targeting CSNK1ε were transfected into two ovarian cancer cell lines with amplified c-MYC expression (IGROC-1 and TOV112D) and two ovarian cancer cell lines with normal, (i.e., low, non-amplified), expression levels of c-MYC (CaOV3 and DOV13) to induce transient knockdown of the CSNK1ε gene. siRNAs targeting UNI served as the negative control and siRNAs targeting KIF11, which is toxic to all cells, served as the positive control. Cell viability was assayed using the Cell Titer Glow Assay at five days post-transfection. The relative viability of the IGROV-1 and TOV112D cell lines were reduced to approximately 55% and 40%, respectively. In contrast, the relative viability of the CaOV3 and DOV13 cell lines were reduced to approximately 95% and 85%, respectively. This data indicates that CSNK1ε is necessary for the viability of ovarian cancer cells that exhibit amplified c-MYC expression.

The impact of stable knock-down of CSNK1ε was assessed for the expression for WNT signal function. To confirm the efficacy of the stable knockdown technique in ovarian cells, Dox-inducible lentivirus constructs encoding shRNAs targeting CSNK1ε were transduced into COLO720E ovarian cells. It is noted that this cell line exhibited the highest c-MYC mRNA levels of all the ovarian cancer cell lines. See FIG. 9B. As illustrated in FIG. 10A, induction of transduced cells with Dox resulted in a drastic reduction in CSNK1ε polypeptide levels, compared to uninduced cells or cells with control lentiviral constructs. Next, to assess the WNT signaling activity, relative O-catenin activity was assayed as described, supra, for COLO720E ovarian cells transduced with the shRNA encoding lentivirus targeting CSNK1ε. Upon Dox induction, the relative β-catenin activity was reduced by approximately one third compared to the uninduced cells. A similar effect on relative β-catenin activity was observed upon administration of IC261, the inhibitor of CSNK1ε. Briefly, COLO720E cells were cultured in 0, 0.67, 3.3, and 6.67 μM IC261. As illustrated in FIG. 10C, the relative β-catenin activity, hence WNT signaling, was reduced by more than two thirds at the higher doses of IC261. This indicates that, similar to the results in neuroblastomas, the effect of CSNK1ε on viability of ovarian cancer cells with amplified c-MYC expression is likely mediated by the WNT signaling pathway.

Inhibition of CSNK1ε by IC261 Selectively Impairs Growth of Ovarian Cancer Lines with Amplified c-MYC.

The effect of CSNK1ε on the cell viability of ovarian cancer lines was investigated in vitro. First, HFF (non-cancer primary cells) with control vector, RMG-1 (normal c-MYC expressing), CaOV3 (normal c-MYC expressing), HFF with cMYC induced (amplified c-MYC expressing), TOV112D (amplified c-MYC expressing), and COLO720E (amplified c-MYC expressing) were exposed to increasing concentrations of IC261. Cell viability was assessed as described above. At 0.5 log μM and above, all of the cells with amplified c-MYC exhibited drastic reduction of relative viability to 25% or less, whereas the normal c-MYC expressing cells exhibited cell viabilities of approximately 75% and above.

Similar assays were performed with an additional panel of ovarian cancer cells, including IGROV-1, PE01, DOV13, OAW42, TOV21G, and SKOV3. The log of the half maximal effective concentration (logIC₅₀) was calculated to reflect half the concentration of IC261 required to results in complete loss of cell viability. The results are provided below in Table 2. Notably, IGROV-1 and PE01, two ovarian cancer cell lines previously established as having some of the highest c-MYN expression levels had the highest logIC₅₀ values, indicating a high potency of IC261 to cause a reduction in cell viability.

TABLE 2 The log of the half maximal inhibitory concentration of IC261 to results in complete loss of cell viability for select ovarian cancer cell lines. log IC₅₀ Cell log IC₅₀ 95% Confidence Intervals IGROV-1 2.767  1.924-3.609 PE01 0.9447 0.6665-1.223 DOV13 0.8505 0.6573-1.044 OAW42 0.8204 0.6288-1.012 TOV21G 0.8162 0.6273-1.005 SKOV3 0.6656  0.4959-0.8354

The effect of CSNK1ε on the cell viability of ovarian cancer cells was then investigated in vivo. Peritoneal carcinomatosis model mice were generated by the intraperitoneal injection of TOV112D/Luc cells. After one week, the mice were randomized into control and experimental groups, which then received daily injections of IC261 or DMSO carrier for three weeks. Weekly Luc imaging was performed for each mouse at the termination of each week of the experiment to monitor the relative viability of cancer cells that have established in the mice. As illustrated in FIG. 11A, mice receiving daily IC261 injections exhibited significantly reduced cancer cell proliferation and viability after two weeks compared to mice receiving DMSO. The difference among treatment groups was much more pronounced by week four. As illustrated in the survival graph in FIG. 11B, the DMSO group and IC261 treatment groups diverged in percent survival starting at day 30 when the DMSO group began to experience drastic mortality. This demonstrates that the inhibition of CSNK1ε reduced the viability of ovarian cancer cells with amplified expression in vitro. Moreover, the inhibition of CSNK1ε in ovarian cancer in vivo resulted in reduced cancer cell viability and proliferation, and ultimately prolonged the life of the subjects.

Analysis of CSNK1ε Inhibitor on the Progression of the Cell Cycle.

Ovarian cancer cell lines with normal (i.e., low) and amplified expression of c-MYC were assessed for the impact of the CSNK1ε inhibitor IC261 on the progression of the cell cycle. CaOV3 cells (normal c-MYC expression) and TOV112D cells (amplified c-MYC expression) were cultured in 1 μM IC261. The cells were assessed for the state of the cell cycle, namely G1, S-phase, and G2, at time points before and 16 and 24 hours after contact with IC261 by Propidium Iodide staining followed by FACS analysis. As illustrated in FIG. 12A, the majority of cells from both cell lines were in the G1 phase of the cell cycle before treatment of IC261. After administration of IC261, the percentage of cells in the G1 phase was drastically reduced. However, the levels were lower for the cells with amplified c-MYC expression. In contrast, very few cells from either cell line were observed in the G2 phase before administration of IC261. See FIG. 12B. Upon administration of IC261, however, a large fraction of the cancer cells with amplified c-MYC expression were arrested at the G2 checkpoint. This trend was not observed for the cancer cells with normal c-MYC expression. This indicates that CSNK1ε function is required for progression of MYC-driven cancer cells to progress from the G2 checkpoint into metaphase. In contrast, for normal c-MYC ovarian cancer cells IC261 only has a small and transient ability to cause cell cycle arrest in G2.

Role of CSNK1ε Inhibitor in Sensitivity of Ovarian Cancer Cells to Treatment with Cisplatin.

Cisplatin, or cis-diamminedichloroplatinum(II) (CDDP), is a chemotherapy drug commonly used to treat numerous types of cancers including ovarian cancer. Cisplatin contains platinum complexes that crosslink DNA, ultimately triggering apoptosis of the cell. However, many treated cancer relapse and display a resistance to cisplatin. Considering the ability of CSNK1ε inhibitors to reduce viability of cells with amplified c-MYC expression, a similar role of CSNK1ε inhibitors on cisplatin resistant cancer cells was investigated. A2780 and A2780-CP70 (resistant derivative), PE01 and PE04 (resistant derivative of PE01) ovarian cancer cell lines were cultured in the presence of increasing doses of cisplatin and the presence or absence of IC261. Cell viability was monitored as described above. As illustrated in FIG. 13A, both A2780 and A2780-CP70 cells response to cisplatin was greatly sensitized by the addition of 1 μM IC-261. It is noted that the c-MYC expression level in A2780 cells is yet undetermined. As illustrated in FIG. 13B, PE01 and the resistant derivative PE04 ovarian cells, both with amplified c-MYC expression, also exhibited a large reduction in cell viability in the presence of low doses of cisplatin when also in the presence of 1 μM IC-261. These results indicate that inhibition of CSNK1ε with IC-261, or other CSNK1ε inhibitors, could be utilized in cases of chemotherapy resistant ovarian cancers.

Conclusion

This example demonstrates that CSNK1ε is required for the viability of ovarian cancer cells with amplified c-MYC expression. Consistent with the role observed in neuroblastoma cells, knockdown of CSNK1ε gene expression and function inhibition of CSNK1ε kinase activity results in reduced WNT signaling, indicating that WNT signaling mediates part of the CSNK1ε's effect on ovarian cell viability of cells with amplified c-MYC expression. Administration of the CSNK1ε inhibitor IC261 results in lower viability and proliferation in vitro and in vivo of ovarian cancer cells with amplified c-MYC expression. Therefore, these results demonstrate that CSNK1ε plays a vital role in the continued viability of MYC-driven ovarian cancers, and is a target for the treatment of MYC driven cancers and cancers otherwise resistant to cisplatin.

While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. 

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A method for inhibiting the growth and/or proliferation of a myc-driven tumor cell comprising the step of contacting the tumor cells with a CSNK1ε inhibitor.
 2. The method of claim 1, wherein the myc-driven tumor cell is of neural origin.
 3. The method of claim 2, wherein the myc-driven tumor cell of neural origin is derived from a primary neuroblastoma tumor, a metastatic neuroblastoma tumor or a brain tumor.
 4. The method of claim 1, wherein the myc-driven tumor cell is an ovarian cancer cell.
 5. The method of claim 1, wherein the myc-driven tumor cell is selected from the group consisting of rhabdomyosarcoma, liver cancer, melanoma, breast cancer, colon cancer, prostate cancer, Burkitt's lymphoma and lung cancer.
 6. The method of claim 1, wherein the tumor cell is contacted in vitro.
 7. The method of claim 1, wherein the tumor cell is contacted in vivo in a mammalian subject.
 8. The method of claim 1, wherein the CSNK1ε inhibitor is a small molecule inhibitor.
 9. The method of claim 8, wherein the CSNK1ε inhibitor is selected from the group consisting of IC261, PF-4800567, and PF-670462.
 10. A method of treating a subject suffering from a tumor comprising myc-driven tumor cells, comprising administering to the subject an amount of a composition comprising a CSNK1ε inhibitor effective to inhibit the growth and/or proliferation of the tumor cells.
 11. The method of claim 10, wherein the subject is suffering from a tumor comprising myc-driven tumor cells of neural origin.
 12. The method of claim 11, wherein the myc-driven tumor cell of neural origin is derived from a primary neuroblastoma tumor, a metastatic neuroblastoma tumor or a brain tumor.
 13. The method of claim 10, wherein the myc-driven tumor cell is ovarian cancer.
 14. The method of claim 10, wherein the myc-driven tumor cell is selected from the group consisting of rhabdomyosarcoma, liver cancer, melanoma, breast cancer, colon cancer, prostate cancer, Burkitt's lymphoma and lung cancer.
 15. The method of claim 10, wherein the subject is further provided one or more additional anti-cancer therapies.
 16. The method of claim 15, wherein the additional anti-cancer therapy comprises chemotherapy.
 17. The method of claim 16, wherein the myc-driven tumor cell is resistant to cisplatin and the CSNK1ε inhibitor renders the cell susceptible to cisplatin.
 18. The method of claim 10, wherein the CSNK1ε inhibitor is a small molecule inhibitor.
 19. The method of claim 18, wherein the CSNK1ε inhibitor is selected from the group consisting of IC261, PF-4800567, and PF-670462.
 20. The method of claim 10, further comprising the step of determining whether the tumor in said subject comprises myc-driven tumor cells prior to treatment with said composition comprising a CSNK1ε inhibitor. 